Development of a new LOPAP instrument for the detection of O3 in the atmosphere

A simple O 3 -LOPAP (Long Path Absorption Photometer) instrument for the selective detection of O 3 in the atmosphere is presented, which is mainly intended to be used as an extension of a recently developed NO 2 -LOPAP. O 3 is sampled in a stripping coil by a selective chemical reaction with the highly absorbing Indigo dye. The reduction of the optical absorption of the dye is detected in a liquid core waveguide. The instrument has a detection limit of 0.4 ppbv, an accuracy of 10%, a precision of 2% for 6 min time resolution and allows the absolute quantification of O 3 according to Lambert–Beer's law. Interferences towards nitrogen oxides (NO and NO 2 ), N 2 O 5 , H 2 O 2 and several VOCs were quantified in the laboratory and found to be negligible for atmospheric conditions. The new instrument was successfully validated against a commercial UV-absorption instrument during an urban field campaign and against the FTIR technique in a smog chamber under complex photosmog conditions. For the UV-absorption instrument significant positive interferences towards aromatic species were observed in the smog chamber.